Research Article Needle microextraction trap for on-site analysis of airborne volatile compounds at ultra-trace levels in gaseous samples Different capillary needle trap (NT) configurations are studied and compared to evaluate the suitability of this methodology for screening in the analysis of volatile organic compounds (VOCs) in air samples at ultra-trace levels. Totally, 22 gauge needles with side holes give the best performance and results, resulting in good sampling flow reproduci- bility as well as fast and complete NT conditioning and cleaning. Two different types of sorbent are evaluated: a graphitized carbon (Carbopack X) and a polymeric sorbent (Tenax TA). Optimized experimental conditions were desorption in the GC injector at 3001C, no make-up gas to help the transport of the desorbed compounds to the GC column, 1 min splitless time for injection/desorption, and leaving the NT in the hot injector for about 20 min. Cross-contamination is avoided when samples containing high VOC levels (above likely breakthrough values) are evaluated. Neither carryover nor contamination is detected for storage times up to 48 h at 41C. The method developed is applied for the analysis of indoor air, outdoor air and breath samples. The results obtained are equivalent to those obtained with other thermal desorption devices but have the advantage of using small sample volumes, being simpler, more economical and more robust than conventional methodologies used for VOC analysis in air samples. Keywords: Needle trap / Screening analysis / Thermal desorption / VOC DOI 10.1002/jssc.201100381 1 Introduction Given the ever greater interest in evaluating atmospheric pollutants for screening purposes at ultra-trace levels, continuous improvement of monitoring methods is required. Analysis of volatile organic compounds (VOCs) in air samples is extensively carried out by sorption on solid sorbents followed by thermal desorption and GC-MS determination (e.g. US-EPA method TO-17 [1], http://www.epa.gov/ttnamti1/files/ambient/airtox/to-17r.pdf). This methodology, which requires highly skilled technicians, makes use of complex and relatively expensive thermal desorption units and needs two desorption steps, increasing the probability of artifact formation. The development of economical and ecological small- scale sample preparation techniques that are able to meet requirements such as enhanced sensitivity and selectivity, robustness and simple handling are desirable. In this respect, solvent-free extraction methods based on the parti- tioning of analytes between gaseous or liquid phase and a stationary phase has become increasingly important and have been widely applied in research over the last decade. As a sample preparation technique intended for VOC analysis, solid-phase microextraction (SPME) has been one of the most successful approaches [2]. However, conventional SPME has the disadvantages of the relative fragility of the exposed coated fused-silica rod and the low sorption capacity of the technique [3]. Although Raschdorf [4] developed the first device based on a needle filled with Tenax sorbent in the 1970s, needle trap (NT) extraction devices have only recently become popular due to their combination of the advantages of SPME (e.g. solventless, fast, sensitive, one-step sample preparation and injection method, small in size and convenient for designing portable devices that can be used in field analysis) with robustness, easier handling during sampling and desorption, and the fact that they permit a high degree of automation and on-line coupling to GC instruments [5]. NT devices can be divided into two different categories: (i) internally coated needles [6–8] and (ii) needles packed with commercially available sorbents [3, 9–21] or chemically synthesized polymers [22, 23]. One commercial approach uses an add-on module packed with a sorbent material positioned between the needle and the syringe (in-tube extraction, ITEX and ITEX-2) [24]. The ITEX device has the drawback of requiring an external thermal desorption unit Monica Alonso Anna Godayol Enriqueta Antico Juan M. Sanchez Chemistry Department, University of Girona, Girona, Spain Received April 28, 2011 Revised June 7, 2011 Accepted June 22, 2011 Abbreviations: NT, needle trap; SPME, solid-phase microextraction; VOC, volatile organic compound Correspondence: Dr. Juan M. Sanchez, Chemistry Department, University of Girona, Campus Montilivi s/n, 17071-Girona, Spain E-mail: juanma.sanchez@udg.edu, juanma.sanchez@udg.es Fax: 134-972418150 & 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim www.jss-journal.com J. Sep. Sci. 2011, 34, 2705–2711 2705